It may be a combination of factors. The US cattle herd is the smallest since 1950, corn is high which has a double effect: more expensive to feed it and if you have ground that can grow corn (or wheat) it is much more profitable use of land than grazing cattle to nearly give away...

Mostly the profit is just not there, for the cattleman at least, in the mainstream cattle business as it has been run in the US in recent years. jmho.

Jim at Dawn